fix(nitro): default to nitro generator and use resolved nitro routes

[danielroe]

🔗 Linked issue

resolves #490

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Although marking nitroGenerator as true by default, we were not actually checking the resolved options. This PR also updates the route generation to be based off nitro's prerender options, not the nuxt ones.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.